This invention relates to a rotational position detecting apparatus for detecting the rotational position of the crank shaft of an internal combustion engine, which can be applied to the ignition system of the engine.
Recently, in the ignition system of an internal combustion engine, it has been proposed to calculate electronically the ignition time in accordance with the operation state of the engine. If the ignition time is set by a rotation angle of the crank shaft between its reference angular position and an angular position for generating a spark after the rotational position of the crank shaft reached the reference angular position, it is necessary to detect the rotational reference position and the rotational angular position of the crank shaft. Conventionally, in order to meet this requirement, the angular position and the reference position have been detected as an angular signal and a reference signal by independent or different sensors respectively. Therefore, in the conventional system the positional relation between the angle and the reference signals varies with an error during manufacture, the number of revolution of the sensor, the temperature characteristic and the threshold voltage of a waveform reshaping circuit. Thus, it occurs that the reference signal and the angular signal are generated within a very short time that an operation processing circuit yields an error signal of angle. There is a further problem that it is difficult to obtain a constant phase between the reference signal and the angle signal.
In a further conventional method, a logical operation was implemented between the angle and the reference signals to determine the angular position and the reference position from the result of the logical operation, however, the conventional methods are not sufficient to overcome the above drawbacks.